The present invention relates to respiratory devices, and more particularly to devices to assist expiration.
Of the various chronic respiratory diseases, the most common is emphysema, which may be defined as alveolar distension and progressive loss of elasticity of the lung and surrounding tissues. Normally, expiration is a relatively passive act, since air is expired due to elastic recoil. Normal breathing is also accompanied by a bellows action of the ribs, particularly the more mobile lower ribs, which are depressed and elevated during expiration and inspiration.
As emphysema progresses in severity, the walls of the alveoli or air cells become less elastic, and a positive pressure becomes required in order to squeeze air from the patient's lungs and accomplish expiration. However, emphysema also causes the ribs to become fixed in an elevated position, and prevents the normal bellows action of the rib cage. Thus, the patient must labor to develop the abnormal pressure necessary to expire while being unable to use the ribs to facilitate breathing. Accordingly, respiration becomes exceedingly difficult for the patient, and virtually all of the thoracic space and most of the accessory muscles of respiration must be utilized to accomplish expiration, resulting in a series of shallow breaths and prolonged periods of expiration.